Rock’n'roll workaholic Dave Grohl’s latest project is his new documentary Sound City, which tells the story of the storied L.A. recording studio of the same name. The project has brought him together with a long list of rock stars, both for interviews in the film and music-making for its soundtrack. And one of them happens to be a Beatle.

One of the most widely-discussed live performances of 2012 was something dubbed “Sir-vana” – the surviving members of Nirvana (Grohl, Krist Novoselic and Pat Smear) + Sir Paul McCartney. At the 12-12-12 Concert, the group performed a new song titled “Cut Me Some Slack,” which makes “Helter Skelter” sound about as hard as “Love Me Do.” The song is the first single from the Sound City soundtrack, Reel To Reel.

Speaking with sister station KROQ’s morning show Kevin & Bean, Grohl explained how “Cut Me Some Slack” came together. As Grohl notes, he’s jammed with Paul “a bunch of times” (the 2012 and 2009 GRAMMYs, among other times over the years), so when he called up Paul to jam about eight months ago while working on Sound City, Macca came right down.

“As we were filming all of these performances, I was just like, ‘Hey dude, why don’t you come down and jam?’,” Grohl said. “He’s like, ‘OK.’ He comes down and he brings the bass that he’s played for 40 years and the Les Paul that there’s only four of in the world. And then he brings his guitar made out of a cigar box – it’s called a cig-fiddle. And he’s like (in a British accent), ‘Oh I think I’ll play this, why don’t you play a bit of drums?’ And we just jammed, and we wrote this song in about and hour and recorded it. We walked in, we jammed it. It came out of nowhere – the best songs happen that way. We recorded it live and put a vocal over it and that was it. It was three hours and it was perfect.”

As for the big premiere of “Cut Me Some Slack” at the 12-12-12 Concert, Grohl explains that it was Paul’s initiation that time.

“He called before the 12-12 thing – maybe a month before – and said, ‘Hey we’re doing this benefit, will you play with me?’” Grohl explained. “I said, ‘Yeah, Foo Fighters are taking a break, but if you wanna play, let me know.’ Then he called a couple days later and said, ‘Hey, why don’t we do that song we recorded with you and Krist and Pat?’”

During his KROQ interview, Grohl praises McCartney at every turn, deeming him “just the sweetest, nicest, most awesome person.” There’s no real element of star-struck-ness, either. “When you meet someone whose music is really important you, their level of fame isn’t important to you,” Grohl said.

He later added: “You have to understand, one of the great things about playing with Paul McCartney or playing with someone like Neil Young is, that generation of musicians, they cherish and respect and value the practice of just going into a room and coming up with something and jamming it and making it a song. There’s not like seven songwriters and seven producers and digital technology or whatever. It’s people getting in a room.”

The whole idea of musicians getting in a room and jamming – and seeing what happens – is at the heart of Grohl’s Sound City doc.

“The movie is really mostly about the human element of music,” Grohl said. “What it’s like to just get together with a person and write a song in a room in a day. It doesn’t have to be perfect but that’s how the magic happens. When you get four human beings playing with each other, you get the Beatles or the Rolling Stones. That’s where the magic happens.”

Supporting his directorial debut, Grohl has assembled an all-star band, the Sound City Players, which features John Fogerty of CCR,  Stevie Nicks of Fleetwood Mac, Rick Nielsen of Cheap Trick, Brad Wilk of Rage Against the Machine and Rick Springfield, as well as Grohl’s Foo Fighters bandmates Pat Smear, Nate Mendel, Taylor Hawkins and Chris Shiflett. The band will premiere tomorrow (January 18) at the Sundance Film Festival, where the film will also make its debut. The Sound City Players will also perform at the Hollywood Palladium January 31. Sound City will screen nationwide this month and next.

For more on Sound City (the movie and the studio), check out Grohl’s full interview with KROQ, which also featured his collaborator Corey Taylor of Slipknot.

- Jillian Mapes, Radio.com